Olefin cracking promoted by methylene chloride



United States Patent 3,296,327 OLEFIN CRACKING PROMOTED BY METHYLENE CHLORIDE Kenneth J. Fresh, Kent, Ohio, assignor to The Goodyear Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Filed Sept. 7, 1962, Ser. No. 222,177

9 Claims. (Cl; 260-680) This invention relates to a promoted cracking process for certain olefins. More specifically it relates to a method of improving the cracking of certain olefins. Most specifically it relates to methods of improving the efliciency of cracking of certain olefin to form specific diolefins and parafiinic hydrocarbons or to form certain other specific olefins.

It is known that certain olefins may be thermally decomposed or cracked by subjecting them to elevated temperatures, for instance olefins which have in their molecular make-up a carbon-carbon bond which is in a position beta to the double bond will under proper conditions of heat, time and pressure undergo a scission of the carbon-carbon bond in the position beta to the double bond. By the terms cracking, decomposing, cracked, or decomposed as employed throughout this specification and claims is meant that the olefin molecule splits into two or more fragments at the carbon-carbon bond which is in a position beta to the double bond. This will be explained in more detail later.

The thermal decomposition or cracking of olefins is usually conducted in a closed zone or reactor and is usually conducted in the absence of oxygen. The temperatures employed usually vary from about 300 to about 1,000 C. Usually this thermal cracking process is conducted while the olefins are in a gaseous state. The olefins may be cracked in relatively pure form or a diluent may be employed.

Employing the most favorable conditions conducive to the cracking of olefins, these conditions being tempera ture, residence time in the cracking zone, the ratio of the olefin to the diluent if any be employed, it has been found that olefins decompose at fairly low yields and to fairly low efiiciency. As employed in this application the term yield is meant to connote the decomposition of the olefin feed stock per pass through the cracking zone and the term efficiency is meant to connote the total decomposition to the desired end product employing well known recycle techniques.

It is therefore the object of this invention to provide a method whereby the yield of the desired products produced by cracking these olefins is increased. Another object is to increase the ultimate yield or efiiciency of the desired product. Another object is to provide a method whereby the residence time in the heating zone and the temperature of the heating zone may be decreased to prevent undesirable side reactions from taking place. Still other objects are to provide cracking promoters which will allow greater yields and greater efficiencie to be obtained in the cracking of these olefins. Still other objects will be apparent as the description proceeds.

To further explain what is meant by a carbon-to-carbon bond in a position beta to the double bond, the following discussion is intended to be illustrative and not restrictive of the scope of this invention. The particular materials 3,296,327 Patented Jan. 3, 1967 which predominate when olefins are cracked depend largely upon the configuration of the particular olefin cracked. By configuration i meant the location of the double bond and the location of the side group on the chain if any be present. It is believed that this best can be illustrated by the following discussion. When an olefin containing 6 carbon atoms with a side group, i.e. a methyl group attached to the second carbonatom of the main or straight portion of the chain, and the double bond is in the 2 position, such as olefin being Z-methyl pentane-2, is subjected to cracking conditions, the predominant products obtained are Z-methyl butadiene-l,3 (isoprene) which is a diolefin, and methane, a paraifin. On the other hand if a 6 carbon olefin such. as Z-methyl pentane-l which has the double bond in the 1 position and the methyl group in the 2 position is. cracked, it will ,yield :as the predominant products two other olefins, isobutylene and ethylene, When still another isomericv hexene, such as 4- methyl pentene-l is cracked, two moles of the olefin propylene are formed. These diiferences in products obtained, when difierent isomeric forms of olefinscontaining the same number of carbon atoms are cracked, are due to the fact that olefins crack at the position beta to the double bond, that is to say the carbon-carbon bond which is two carbon atoms removed from the double bond, is the carbon-to-c'arbon bond at whi'chthe scission occurs. There are certain olefins which do not contain in their molecular make-up a carbon-carbon bond in the position beta to the double bond and, therefore, do not undergo the same reactions when subjected to thermal decomposition conditions. These olefins are ethylene, propylene, butene-2, isobutene, 2-methyl butene-2, and 2,3-dimethyl butene-Z, and are usually referred to as refractory olefins. Since these olefins do not undergo similar chain scission as do olefins which contain in their molecule a carbon-tocar-bon bond in the beta position to the double bond, these refractory olefins are not considered to be within the scope of the olefins which are to be cracked in accordance with this invention.

It has been found that the objects of this invention are accomplished by subjecting olefins, which have in their molecule a carbon-carbon bond which is in a position beta to the double bond, to conditions of temperature and time suitable or sufiicient to cleave the carbon-carbon bond which is in a position beta to the double bond, while said olefin is in the presence of an olefin cracking promoter comprising methylene chloride.

In general the practice of this invention may be carried out in any conventional manner which is usually em loyed in the thermal cracking of olefins.

Generally the conditions which may be employed in the practice of this invention may vary widely, for instance the cracking temperature may vary broadly from about 400 C. to about 900 C. However, more preferred cracking temperatures are from about 600 C. to about 750 C. The time in which the olefins are in the cracking zone may range broadly from about 0.001 to about 3.0 seconds. However, it is more preferable to employ times varying from about 0.05 to about 0.5 second. These times which are referred to are usually called residence times and are defined as the time required for one mol of gas whether it be pure olefin or in mixture with the diluents to pass through the cracking zone.

As was stated above, generally olefins are cracked either as pure hydrocarbons or as mixtures with other a diluent gases. These diluent gases may be such materials as steam, carbon dioxide, hydrogen, parafiins, the refac tory olefins, or any other inert gaseous substance which does not materially affect the cracking process or react with either the feed stock or products other than to act generally as a diluent. The ratio of this diluent gas may be widely varied depending on conditions, but it is usually employed in mol ratios of from about 0.5/1 to about 15/1 moles of diluent per mol of olefin. If more than about 15/1 mol ratio is employed, the process tends to become uneconomical. Therefore, it is preferred to usea diluent to olefin mol ratio ranging from about 2/1 to about 4/1.

The pressure employed in the cracking zone may be varied from a low of 10 milliliters of mercury to 500 pounds per square inch gauge or even higher. However, it is usually preferred that the pressure range from about atmospheric to about 100 p.s.i. with about 1-2 atmospheres being preferred.

As was stated previously the olefin cracking promoter employed in this invention is methylene chloride. The amount of methylene chloride employed in the practice of this invention has not been found to be too critical. Of course, sufficient promoter should be employed to obtain some beneficial effect, on the other hand, for the sake of economy, no more promoter should be employed than is necessary. Generally it has been the practice to employ from about 0.5 to about 50 mole percent of methylene chloride based on the total moles of olefin desired to be cracked, with about 5 to mol percent being preferred.

The practice of this invention is illustrated by the following experiments which are to be interpreted as representative rather than restrictive of the scope of this invention. The results and conditions of the cracking experiments are reported in table form.

All of the cracking experiments were performed in a reactor assembly consisting of a hairpin coil prepared from fli-inch OD. 316 stainless steel tubing. This coil reactor was immersed in a bed of fluidized heat transfer powder which was microspheroidal silicia-alumina cracking catalyst. The heat transfer powder was heated both by electrical resistance heaters and by combusting a natural gas flame in the fluidized powder bed. The temperature gradient from top to bottom of the bed was never more than 5 to 6 C. and the gradient from the fluidized bed to the tube walls was about 5-6 C. The temperatures within the fluidized bed were measured by conventional thermocouple techniques as were the temperatures within the cracking zone. The procedure employed was to bring the heat transfer powder up to about 500 C. employing the electrical resistance heaters while fiuidizing the heat transfer powder with air. Then the natural gas burner was employed to bring the heat transfer powder up to the desired cracking or operating temperature. The methylene chloride was added to the olefin feed stream. (It could have been added seperately to the cracking reactor.) The water and the olefin were pumped at the proper rates necessary to produce the H O/hydrocarbon ratio desired and to give the desired residence time of the materials in the cracking zone or cracking reactor. When all variables had been adjusted to give the desired operating conditions the products resulting from the cracking operation were collected by means of cooled receivers, if liquid, and were metered at atmospheric and room temperature conditions, if gas. The products were analyzed for content and yields by conventional analytical methods. Conventional recycle techniques were employed to obtain the ultimate yield.

The results of each of the experiments in the following examples as well as the operating conditions are reported in tables below. Column 1 is the experiment number; column 2 is the residence time in seconds; column 3 is the temperature employed in the cracking operation in degrees Centigrade; column 4 is the material employed as the cracking promoter with the amount em-. ployed in mol percent based on the olefin to be cracked; (Where no promoter was employed this column lists none); column 5 is the mol percent yield of isoprene per pass based on the B-methyl pentene-Z charged; column 6 is the reaction efficiency or ultimate yield and is the amount of isoprene obtained based on the 3-methyl pentene-Z charged using conventional recycle techniques.

Example In this example 3-methyl pentene-2 was the olefin cracked. Steam was used as a diluent at a mole ratio of water to hydrocarbon of approximately 3/ 1.

Experi- Time Tempera- Promoter Yield Efiioieney ment No. ture 1 O. 15 675 None 15. 33 60. 5 2 0. 15 676 CHzCh-5%. 25. 40 68. 4 3 0. 15 672 CH2C19%. 26. 69. 0

From the above experiments it can 'be seen that the practice of this invention (as exemplified by Runs 2 and 3) shows a marked increase in the yield of isoprene obtained per pass and a higher reaction selectivity (efficiency) to isoprene than that obtained in a true thermal cracking operation (exemplified by Run No. 1).

Other similar improvements may be obtained when the general techniques of these examples and the other spe-.

' cific teachings mentioned elsewhere in this application are applied to other olefins having in their molecules a carbon-carbon bond in a position beta to the double bond.

The list of olefins set forth below are representative examples of olefins, the cracking of which may be enhanced by the promoter of this invention.

Representative among the olefins which will decompose ene-l; 3,3-dimethyl hexene-l; 2,5-dimethyl hexene-Z; 3,5-

dimethyl hexcne-Z; 4-methyl-2-ethy-l pentene-l; 2,3,4-trimethyl pentene-l; 3,3,4-trimethyl pentene-Z; Z-m-ethyl octene-2; 3-methyl octene-Z; 3,3dimethyl heptene-l; 2,5-

dimethyl heptene-Z; 2,6-dimethyl heptene-Z; 5-methyl-2- othyl hexene-l; 3,3,5-trimethyl hexene-l; and 2,5,5-trimethyl hexene-Z.

Representative among the olefins which will decompose to form predominantly Z-ethyl butadiene-l,3 when cracked in accordance with the practice of this invention are 3-ethyl pentene-2; 2-ethyl pentene-2; 3-ethyl hexene-Z; 3-meth- :rl-Z-ethyl pentene-l.

Representative among the olefins which will decompose to form predominantly 2,3-dimethyl butadiene-1,3 rwhen cracked in accordance with the practice of this invention are 2,3-dimethyl pentene-2; 3-methyl-2-ethyl butene-l; 2, 3,3-trirnetl1yl butene-l; 2-isopropyl pentene-l; 2,3,3-trimethyl pentene-l; and 2,3-dimethyl heptene-2.

Representative among the olefins which will decompose to form predominantly 3-methyl pentadiene-l,3 when cracked in accordance with the practice of this invention are 3-methyl =hexeue-3; 3-methyl heptene-3; 3,4-dimethyl hexene-2; 3,6-dimethyl heptene-3.

Representative among the olefins which will decompose to form predominantly 2-methyl pentadiene-l,3 and 4- methyl pentadiene-l,3 when cracked according to the practice of this invention are 2,4-dimethyl pentene-Z; 2- methyl heptene-3; 4,4-dimethyl hexene-Z; Z-propyl pentene-Z; 2-methyl-3-ethyl pentene-l; 2,6-dimethyl heptene- 3 and 2-propyl hexene-l.

Representative among the olefins which will decompose to form predominantly piperylenes when cracked in accordance with the practice of this invention are hexene-3; 4-methyl pentene-Z; heptene-3; 4-methyl hexene-Z; octene- 3; 4-methyl heptene-2; 6-methyl heptene-3; 3-ethyl hexene-1; 4-methyl-3-ethyl pentene-Z; 4,5-dimethy-l heptene- 2; and 4,5,5-trimethyl hexene-Z.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein Without departing from the spirit or scope of the invention.

What is claimed is:

1. An isoprene producing process which comprises providing a mixture of (a) at least one olefin from the group of 2-methyl pentene-2; 3-methyl pentene-2; 2-ethy-l butene-l; 2,3-dimethyl butene-l; Z-methyl hexene-Z and S-methyl hexene-2 and (b) at least 0.5 mol percent, based on the total mols of said olefin, of methylene chloride, subjecting said mixture to temperatures ranging from about 400 C. to about 900 C. for periods of time ranging from about 0.05 to about 0.5 second at pressures not exceeding about 100 psi, to cleave the 'carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming isoprene and recovering said isoprene.

2. The method of preparing isoprene which comprises subjecting 3-methyl pentene-Z in the presence of steam at a mole ratio of water to hydrocarbon of approximately 3/1 and methylene chloride in the amount of from about 5 to 10 mole percent based on the total moles of said 3- methyl pentene-Z to temperatures varying from about 600 to about 750 C. for times varying from about 0.05 to about 0.5 second, thereby cleaving the carbon-to-carbon bond in the position beta to the double bond to form isoprene.

3. The method of preparing isoprene which comprises subjecting 2-methyl pentene-2 in the presence of steam at a mole ratio of water to hydrocarbon of approximately 3/1 and methylene chloride in the amount of from about 5 to 10 mole percent based on the total moles of said 2- methyl pentene-2 to temperatures varying from about 600 to about 750 C. for times varying from about 0.05 to about 0.5 second, thereby cleaving the carbon-to-carbon bond in the position beta to the double bond to form isoprene.

4. A butadiene-1,3 producing process which comprises providing a mixture of (a) at least one olefin from the group of pentene-Z and hexene-2; and (b) at least 0.5 mol percent, based on the total mols of said olefin, of methylene chloride, subjecting said mixture to temperatures ranging from about 400 C. to about 900 C. for periods of time ranging from about 0.05 to about 0.5 second at pressures not exceeding about 100 p.s.i., to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming butadiene-1,3 and recovering said butadiene-1,3.

5. A 2-ethy1 butadiene-l,3 producing process which comprises providing a mixture of (a) at least one olefin from the group of S-ethyl pentene-Z; 2-ethyl pentene-Z and 3-ethyl hexene-Z and (b) at least 0.5 mol percent, based on the total mols of said olefin, of methylene chloride, subjecting said mixture to temperatures ranging from about 400 C. to about 900 C. for periods of time ranging from about 0.05 to about 0.5 second at pressures not exceeding about p.s.i., to cleave the carbon-to-car-bon single bond which is in the position beta to the double bond of said olefin, thereby forming 2-ethyl butadiene-1,3 and recovering said 2-ethyl butadiene-l,3.

6. A piperylene producing process which comprises providing a mixture of (a) at least one olefin from the group of hexene-3; 4-methyl pentene-2; heptene-3 and 4- methyl hexene-2 and (b) at least 0.5 mol percent, based on the total mols of said olefin, of methylene chloride, subjecting said mixture to temperatures ranging from about 400 C. to about 900 C. for periods of time ranging from about 0.05 to about 0.5 second at pressures not exceeding about 100 p.s.i., to cleave the carbon-tocarbon single bond which is in the position beta to the double bond of said olefin, thereby forming piperylene and recovering said piperylene.

7. A 2,3-dimethyl butadiene- 1,3 producing process which comprises providing a mixture of (a) at least one olefin from the group of 2,3-dimethyl pentene-2; S-methyl-2-ethyl butene-l and 2,-3-dimethyl heptene-Z and (b) at least 0.5 mol percent, based on the total mols of said olefin, of methylene chloride, subjecting said mixture to temperatures ranging from about 400 C. to about 900 C. for periods of time ranging from about 0.05 to about 0.5 second at pressures not exceeding about '1-00 p.s.-i., to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming 2,3-dimethyl butadiene-l,3 and recovering said 2,3-dimethyl butadiene-LB.

-8. A S-methyl pentadiene-1,3 producing process which comprises providing a mixture of (a) at least one olefin from the group of 3-methyl hexene-3; 3,4-dimethyl hexene-2 and 3-methyl heptene-3 and -(b) at least 0.5 mol percent, based on the total mols of said olefin, of methylene chloride, subjecting said mixture to temperatures ranging from about400" C. to about 900 C. for periods of time ranging from about 0.05 to about 0.5 second at pressures not exceeding about 100 psi, to cleave the carbonto-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming '3-methyl pentadiene-l,3 and recovering said 3-methyl pentadiene- 1,3.

9. A 2-methyl pentadiene-l,3 producing process which comprises providing a mixture of (a) at least one olefin from the group of 2,4-di-methyl pentene-2; 2-methyl heptene-3 and 2-propyl pentene-Z and (b) at least 0.5 mol percent, based on the total mols of said olefin, of methylene chloride, subjecting said mixture to temperatures ranging from about 400 C. to about 900 C. for periods of time ranging from about 0.05 to about 0.5 second at pressures not exceeding about 100 p.s.i., to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin, thereby forming 2- methyl pentadiene-1,3 and recovering said 2-methyl pentadiene-1,3.

References Cited by the Examiner UNITED STATES PATENTS 1,925,421 9/ 1933 Van Peski 26068'3 2,063,133 12/ 1936 Tropsch 260-683 2,417,105 3/ 1947 Folkins 2606'83 3,209,048 9/1965 Burk et a1 260680 FOREIGN PATENTS 588,870 7/1960 Belgium.

PAUL M. COUGHLAN, JR., Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner. 

1. AN ISOPRENE PRODUCING PROCESS WHICH COMPRISES PROVIDIDNG A MIXTURE OF (A) AT LEAST ONE OLEFIN FROM THE GROUP OF 2-METHYL PENTENE-2; 3-METHYL PENTENE-2; 2-ETHYL BUTENE-1; 2,3-DIMETHYL BUTENE-1; 2-METHYL HEXENE-2 AND 3-METHYL HEXENE-2 AND (B) AT LEAST 0.5 MOL PERCENT, BASED ON THE TOTAL MOLS OF SAID OLEFIN, OF METHYLENE CHLORIDE, SUBJECTING SAID MIXTURE TO TEMPERATURES RANGING FROM ABOUT 400*C. TO ABOUT 900*C. FOR PERIODS OF TIME RANGING FROM ABOUT 0.05 TO ABOUT 0.5 SECOND AT PRESSURES NOT EXCEEDING ABOUT 100 P.S.I., TO CLEAVE THE CARBON-TO-CARBON SINGLE BOND WHICH IS IN THE POSITION BETA TO THE DOUBLE BOND OF SAID OLEFIN, THEREBY FORMING ISOPRENE AND RECOVERING SAID ISOPRENE. 